When you initially log in or whenever you have new accounts installed, you should verify that your mail is being forwarded properly, to a single location. If your .forward files don't all ultimately point to a single location, you will probably notice that you're not getting all your mail, as some of it will begin to collect on alternate machines. This is because there is no central department mail server that receives all of our mail. Individual groups have their own mail servers, so it's important to pick one server and make sure all your mail is going there.
If you end up with accounts in multiple locations, keeping track of all your ~/.forward files can be a real pain. showforwards lets you check all your ~/.forward files at once, so you can verify that they all point to one location.
For a more detailed discussion of the showforwards command, see the chapter on the mail system.